A transponder-provided pneumatic tire has been known so far in which a transponder storing the information peculiar to a tire (ID information) in an electronic circuit is set for the purpose of automation of manufacturing of tires, and follow-up, and classification, inventory control, shipping, statistical process control, field engineering, theft prevention, maintenance, regeneration control, application to other tires, and identification of tires under and after manufacturing of them (e.g. "transponder-provided pneumatic tire" disclosed in the official gazette of Japanese Utility Model Application Laid-Open No. 2-123404).
The ID information stored in a transponder can include the size, type, manufacturing factory name, manufacturing line number, manufacturing serial number, manufacturing date, shipping date and the like of a tire.
To increase the communication distance between an interrogator and a transponder, it is necessary to increase the interrogation signal (challenge signal) of the interrogator or increase the transmit-receive antenna of the transponder in size. However, this method is not practical when considering the restrictions based on laws and regulations (e.g. the Wireless Telegraphy Act.) and influences of electromagnetic waves on neighboring persons and electronic units.
Moreover, because the transponder uses the energy of an interrogation signal emitted from the interrogator as the driving power source of internal circuits and the energy of response signals, it is a problem how to efficiently receive the energy of limited interrogation signals. This is because the received energy quantity greatly influences the communication distance.
However, when setting the transponder into a tire, it is not preferable to increase the size of an antenna in order to increase a communication distance because the transponder serves as a foreign matter for the tire and thereby, the function of the tire may be deteriorated.
For example, the official gazette of Japanese Patent Laid-Open No. 5-169931 ("pneumatic tire provided with a transponder") discloses a transponder-provided tire which identifies a tire by using the bead wire in a tire as the primary winding of a transformer and thereby, using the coil antenna of the transponder as a secondary winding.
In this case, transfer of an interrogation signal and a response signal between an interrogator and the transponder uses the electromagnetic induction phenomenon. Therefore, the coil antenna of the transponder serving as a secondary winding becomes elliptic and large one provided along a bead core because it is necessary to interlink the magnetic flux emitted from the bead wire serving as a primary winding as much as possible. However, the large antenna of the transponder is not practical because a tire may be damaged while the tire runs or it is formed or cured.
The present invention is made to solve the above problems and its object is to provide a reliable transponder and a transponder-provided pneumatic tire which are not broken while the tire runs or it is formed or cured by using various metallic members used in the tire as an antenna directly connected to the transponder and thereby, further decreasing the size of the transponder. Moreover, it is another object of the present invention to provide a transponder-provided pneumatic tire capable of increasing the communication distance between an interrogator and the transponder without increasing the transmission output of the interrogator.